The present invention relates to an engine drive oil pump, and more particularly, to an oil pump having function of reducing the pulse pressure within an outlet port.
Japanese document JP-U 2-43482 discloses a trochoid oil pump wherein a plurality of pump chambers defined between inner and outer rotors continuously increase or decrease in volume under an engine driving force to pressurize oil inhaled therein through an inlet port and discharge it to an outlet port. A closed groove is arranged above the outlet port, having an upper portion serving as an air chamber for accumulating air.
Since this oil pump has air chamber formed at the outlet port, the pulse pressure produced by the pump chambers which open successively into the outlet port to discharge oil can be absorbed by the damping action provided by the air chamber.